JavaScript加减计算方法和显示千分位

        Math.formatFloat = function (f, digit) {
            var m = Math.pow(10, digit);
            return parseInt(f * m, 10) / m;
        };

        function formatThousand(num) {
            num = num + "";
            var re = /(-?\d+)(\d{3})/;
            while (re.test(num)) {
                num = num.replace(re, "$1,$2");
            }
            return num;
        }